1. Field of the Invention
The invention is drawn to compositions and methods effective for controlling termites and soil-dwelling or subterranean insects.
2. Description of the Prior Art
Subterranean termites (ST) are destructive pest insects that destroy cellulosic material such as trees and wood structures. In the United States ST are estimated to cause $1 billion in damage annually, including prevention and repair costs (Su and Scheffrahn, 1990). A predominant species of ST, the Formosan subterranean termite (FST), Coptotermes formosanus (Shiraki), has become an economically significant nest in the United States in the past 50 years. This impact is due to the massive size of their colonies which can contain tens of millions of individuals, their propensity to attack several species of living trees, and their high rate of reproduction.
Termite infestations are very difficult to treat due to the cryptic nature of these insects. Formosan termites are even more difficult to control due to the massive numbers of individuals in their colonies and their propensity to attack living trees where nests have been found. Prior to 2005, it was estimated that over 50% of the trees in New Orleans, La. were infested with Formosan subterranean termites. As the Formosan termites consume the heartwood of these trees, the trees are weakened and often fall during strong winds. Formosan termite infestations can also lead to the establishment of carton nests in wooden structures such as homes provided a source of water is available, thus alleviating their need to return to the ground.
The most successful existing methods for control of subterranean termites are preventive rather than remedial. These include barrier treatments to structures and the preemptive treatment of wood materials with chemicals to prevent termite attack. These however have drawbacks. Physical barriers are not compatible for retrofitting on many existing constructions and may not be completely effective, and chemical treatments are only partially effective and last only about five years.
Organochlorine compounds were previously used to control Formosan termites, but their sale was banned in 1988. Replacement chemicals are not as persistent (Su et al., 1998). In addition, by disturbing soil around a structure when landscaping or compensating for soil subsidence the chemical barriers can be compromised and allow termite access to the structure (Su et al., 1990). Su et al. (1998, supra) review some alternative control methods including non-repellant termiticides and bait technology. In order for these techniques to work they must not repel termites, must be easily transferable in or on termite bodies and have delayed toxicity which allows transfer from foraging workers to members of the termite colony that do not forage (Su et al., 1996 and 1998, supra).
Interest in biological insect and fungal control agents is growing as a consequence of concerns regarding chemical pesticide use. The biological control of insect pests presents an alternative means of pest control which can play a role in integrated pest management and reduce dependence on chemical pesticides. Generally, biological agents have little adverse ecological impact due to their specificity for the target host. Also, long term environmental hazards and health concerns are not a factor with biological control agents because chemical residues are not present.
Paecilomyces fumosoroseus is an entomopathogenic fungus with potential for use in controlling several insect pests (Osborne, 1990; Altre and Vandenberg, 2001; Vandenberg et al., 2001; Shimizu and Yamaji, 2002). Our laboratories previously identified P. fumosoroseus as an effective biological control agent for use in controlling subterranean termites (Wright et al., 2003). Other biological agents, particularly fungi, have also been described for use against termites. Milner et al. (1966) review a wide variety of fungi that have been reported as potential pathogens to termites. Pathogenicity of strains of both Metarhizium anisopliae (Metschnikoff) Sorokin and Beauveria bassiana (Balsamo) Vuillemin have been demonstrated in laboratory colonies of C. formosanus [Delate et al. (1995), Wells et al. (1995), and Jones et al. (1996)] discovered that small numbers of B. bassiana and M. anisopliae spores can be spread throughout a C. formosanus colony without being detected by the termites. Conditions in a termite nest, moderate temperature and high humidity, are conducive to the growth of fungal species and are important factors in fungal survivability and propagation [Kramm et al. (1982), Ignoffo (1992), and Stimac et al.] teach a novel B. bassiana strain (ATCC 20872) useful in controlling termites of the genera Cryptotermes, Coptotermes, Incistermes, and Reticulitermes. The contents of each of above-mentioned publications are hereby incorporated by reference herein.
However, despite these advances, the success of an entomopathogenic biological control agent depends largely on the ability of the agent to be delivered to and establish itself in the insects' environment. The use of microbial agents, such as the blastospores of P. fumosoroseus, for controlling Formosan termite infestations, requires that these agents contact the termite, germinate, and infect the termite. Typically, biological control agents are formulated as a wettable powder, wettable granule or liquid suspension (Fravel et al., 1998). While these types of formulations are suitable for most environments, some insects reside in areas difficult to reach, such as the cavities in trees, walls of buildings or subterranean environments. Although the control of insects in trees and walls of buildings is currently accomplished with the application of chemical pesticides in foam formulations, at present, no commercially available foaming agents which are broadly compatible with microbial biological control agents have been described.